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Old 03-12-2009, 12:33 PM   #1
lkvee
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Default Has the Dell 1800FP exhibited bad caps?

When I turn mine on, the power light goes green, and I can't see an image or a backlight. After the customary amount of time has passed, the power light will turn to amber and the backlight will activate. After a few seconds that backlight will go out.

I can change the behavior of the backlight and power LED by adjusting the contrast. I'm not sure if I can do so by adjusting the brightness.

I'm aware of an issue with ICE2AS01. During some discussion offline, I was told this circuit essentially regulates all of the power going to the monitor, so if I'm getting SOME power, then the issue could lie elsewhere.

I just want to confirm the capacitors on this thing are good enough for government. When I opened it up, I failed to find any capacitors whose tops have blown, and I don't believe I found any with electrolyte oozing from the bottom.

Thanks for reading!
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Old 03-12-2009, 01:27 PM   #2
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Default Re: Has the Dell 1800FP exhibited bad caps?

Often caps will fail without any obvious signs. Some brands have a bad reputation, others are usually OK.

I am intrigued by your description of the sequence of events. A common failure mode is:
1. Monitor power is plugged in (signal cable is not connected)
2. Power LED turns on (green).
3. Backlight turns on, 'No signal' or similar message appears
4. Backlight turns off, Power LED remains green.
5. Power LED goes orange.

You imply the power LED goes orange BEFORE the backlight turns on. This is unusual.

Pictures of the circuit board would be a big help, particularly from different directions so we can identify the manufacturers of the caps.

PlainBill
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Old 03-12-2009, 09:11 PM   #3
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Post Re: Has the Dell 1800FP exhibited bad caps?

Quote:
Originally Posted by PlainBill
Often caps will fail without any obvious signs. Some brands have a bad reputation, others are usually OK.

I am intrigued by your description of the sequence of events. A common failure mode is:
1. Monitor power is plugged in (signal cable is not connected)
2. Power LED turns on (green).
3. Backlight turns on, 'No signal' or similar message appears
4. Backlight turns off, Power LED remains green.
5. Power LED goes orange.

You imply the power LED goes orange BEFORE the backlight turns on. This is unusual.

Pictures of the circuit board would be a big help, particularly from different directions so we can identify the manufacturers of the caps.

PlainBill
I don't get it either. It sounds like no other thing I've heard or seen. Would be interesting to see what is causing the problem. As per PlainBill suggestion, post some pictures. And to see or know if the caps are good or not so good, their values, series, brand and V rating would help us to help you.
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Old 03-18-2009, 12:13 AM   #4
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Default Re: Has the Dell 1800FP exhibited bad caps?

My eyes didn't have the greatest focus, so I may be misdescribing some of the capacitors. I saw:

KMG at 2200uF and 16V (2)
KMG at 2200uF and 10V
SAMWHA/RD at 2200uF and 10V (2)
PNA at 1000uF and 16V
SAMWHA/RD at 470uF and 25V

I don't mind taken this monitor apart again - disassembly was easy enough. I hope the pictures helped.
Attached Images
File Type: jpg Dell1800FP.01.jpg (509.4 KB, 129 views)
File Type: jpg Dell1800FP.04.jpg (286.5 KB, 79 views)
File Type: jpg Dell1800FP.02.jpg (390.7 KB, 75 views)
File Type: jpg Dell1800FP.05.jpg (284.9 KB, 86 views)
File Type: jpg Dell1800FP.03.jpg (490.2 KB, 79 views)
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Old 03-18-2009, 12:23 AM   #5
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Post Re: Has the Dell 1800FP exhibited bad caps?

Quote:
Originally Posted by lkvee
My eyes didn't have the greatest focus, so I may be misdescribing some of the capacitors. I saw:

KMG at 2200uF and 16V (2)
KMG at 2200uF and 10V
SAMWHA/RD at 2200uF and 10V (2)
PNA at 1000uF and 16V
SAMWHA/RD at 470uF and 25V

I don't mind taken this monitor apart again - disassembly was easy enough. I hope the pictures helped.
None bulged at first sight.
You should check your voltage outputs at the connector between the PSU and the VBoard, to see what is getting feed to it.
If replaced, I think that you can change all the 2200uf for 16v ones (you have 10 and 16v).
Better to wait for confirmation or suggestion from a (more) senior member (PCBONEZ, Toasty, Wizard, anyone there ...?)
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Old 03-18-2009, 01:44 AM   #6
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Default Re: Has the Dell 1800FP exhibited bad caps?

Replace IC 901 (ICE2AS01) C907 47uF 50V.
to check ic901 get data sheet
Check across the pads of where the zener diode would go (if it was there) next to the ICE PWM chip, I think it goes to pins 6 & 7.
If you have < 2vdc there, and have ~175 across the large cap, the PWM chip is probably shorted. Remove the ICE chip and check again, you should have ~50vdc with it out if it is shorted.
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Old 03-18-2009, 05:51 AM   #7
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Default Re: Has the Dell 1800FP exhibited bad caps?

also resolder the rectifiers and the inverter switch fet.
bad solder joints is what pops the ICE.
i have seen many high esr caps on these too.
replace ALL lytics.
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Old 03-18-2009, 06:16 AM   #8
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Default Re: Has the Dell 1800FP exhibited bad caps?

[QUOTE=FIXITNOW]Replace IC 901 (ICE2AS01) C907 47uF 50V.
to check ic901 get data sheet
Check across the pads of where the zener diode would go (if it was there) next to the ICE PWM chip, I think it goes to pins 6 & 7.
If you have < 2vdc there, and have ~175 across the large cap, the PWM chip is probably shorted. Remove the ICE chip and check again, you should have ~50vdc with it out if it is shorted.[/QUOTEHello

Hello FIXIT
As it is quiet on monitor forum at the moment,can I ask a question,
I dont know much about measuring boards with M/Meter when powered up, I have not done it before, you mention above that the big cap is measured AC, I was of the understanding that the bridge rectifier turned AC to DC , so as the big cap is after B/Rectifier it would be DC, but obviously not can you tell me were the AC ends and DC begins, in laymans terms if you have a spare moment
thxs in advance
bob
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Old 03-18-2009, 09:23 AM   #9
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Default Re: Has the Dell 1800FP exhibited bad caps?

~in the case of my note means approxmently (sorry an english electronics term)
ie ~ 50v dc (approxmently 50v dc)
~175 dc across the large cap if supply 110v AC
if 240v AC nearer 340v dc
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Old 03-18-2009, 11:05 AM   #10
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Default Re: Has the Dell 1800FP exhibited bad caps?

A sine sign means AC. Next time use @ for appox symbol.

Cheers, Wizard
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Old 03-18-2009, 04:07 PM   #11
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Default Re: Has the Dell 1800FP exhibited bad caps?

i think possible problem is in eeprom or mcu on main a/d (scaler) board
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Old 03-27-2009, 12:39 AM   #12
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Default Re: Has the Dell 1800FP exhibited bad caps?

The Dell UltraSharp 1800FP has at least 3 flaws including some bad caps.

1) Diode solder connections break
2) Bad caps on display board
3) Bad caps on power supply

On the LG 6870T445D10 power supply the output diode array D906 and D903 solder can break which burns out the ICE2AS01 PWM. Some have mentioned there is a missing zener diode ZD902 that would protect against this but so far no values have been put forth though it seems quite easy to do. Add a half volt to the max value on the data sheet. Measure the working voltage to ensure that we aren't already above the max.

I resoldered power supply D906, D903 and the input cap C905. My ICE2AS01was not damaged. Some recommend removing all existing solder before resoldering.

On logic board L1800FPK 6870T573A62 L1800F containing chips THine THC63LVD823 and Genesis gm5120, the SamYoung SMD caps with the 3 point swirl logo C739 and C207 10uf 16v K3L K3o K3α are bad. On the first logic board which I eventually burned out, they measure 10, 20 ESR ohms out of circuit. On the working eBay replacement they measure 1.6, 3.6 ohms in circuit and 8.5, 8.6 ohms out of circuit so the replacement board wouldn't have lasted long. They are the same type and size as the two 10f 16v C604 and C507 caps found on the infamous 1702FP BN41-00101A AD video board which cause a blank/black screen and flashing leds. Fixing that board is what gave me the idea to check them here on the 1800FP board guessing that they might be from the same bad batch. The logic board SMD caps are all grounded on the negative side so are easy to test and they test fairly well in circuit. Attach one probe to any ground then hit each positive with the other probe. None of the caps test to be in parallel so if any are bad the board has lost some important function and will not display an image.

I replaced video board C739 and C207 with some 10uf 50v non SMD caps commonly found in junk ATX power supplies. C817 had a suspiciously high ESR in circuit but tested fine out of circuit.

Had I not broken the first logic board with too much testing on a bad power supply, replacing C739 and C207 might have repaired it. At first it was able to light the power led yellow/red/orange though no logo ever showed. By the time I learned that the unsafe and unfixed LG power supply required servicing, my testing killed the the logic board completely. The burned out logic board does not light the power led at all.

Eventually I figured out that the 5v caps in the LG power supply were no good. They were not bulged or leaking and had decent ESR at 0.11 ohms. The way I figured it out was to measure the output voltage with and without a top quality capacitor in parallel. Without the extra cap the 5v line measured 4.71v running on the SamYoung 10v 2200uf group, a stretch for 10% tolerance. With my motherboard grade cap the 5v line measured 4.92v. After replacing the three 5v caps the final was 4.96v. The PWM reducing the voltage tells me that the ripple was too high and my good cap cut the ripple down so the PWM could raise the average voltage measured by the DVM.

I replaced power supply C907 and C924 in the PWM section. I replaced C918, C915, and C914 on the 5v rail. I replaced C913 on the 12v rail. Sam Young C911 and C921 on the 12v rail tested fine.

Though I have no proof I suspect that the 1800FP LG power supply is a poor design and the slightest amount of bad ESR in the 5v caps sends the voltage of death into the logic board just like any good Bestec would do to an unwary eMachines board. Fix all power supply problems before testing anything.

I had no problems on the high voltage inverter. This 1800FP is definitely UltraSharp.

Dropping a good cap in parallel with the rest is a fast way to troubleshoot circuits that are partially working. Just as with different ohm resistors in parallel, the cap with the best ESR in a parallel circuit takes the lion's share of the load. If the circuit springs to life you have found the problem.

I fixed a bunch of IWE1100-A access points this way where the 48v POE to 5v converter board wasn't working. The output voltage was about 1.7v and the LEDs were dim or dark. Most worked with an alternate 5v supply in the power port. After about an hour of testing that didn't reveal much other than that nothing was burned out in the voltage converter and it should work. Out of frustration I placed a new cap across the output caps. The green power L.E.D. lit up and the WiFi unit would have been functioning if it hadn't started at a brain dead 1.7v. A few caps later and they were all fixed. There are 5 of the same brand bad caps on the IWE1100, 2 on the POE converter and 3 on the main board. The voltage converter caps see more heat so wear out faster. The mainboard caps should fix problems with unit lockup. The voltage converter caps were hard to get out and even harder to insert so I placed long lead Rubycon 2200uf caps in the cavity where the old caps were and surface mounted the leads. Those units should have a long life now.
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Old 05-25-2009, 08:19 PM   #13
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Default Re: Has the Dell 1800FP exhibited bad caps?

I am rapairing a DELL 1800FP display. The problem is that when VGA signal is connected, the backlight randomly turns on/off about half to several seconds apart.

The logic boad has two caps with high ESR: C739 and C207 as noted by severach. I added parallel capacitors to fix them. However the probelm still persist. C739 measure good 5.0V.

All caps in the power supply board measure good ESR.

The backlight will turn on persistently if the VGA cable is unplugged. This showed that the inverter board is OK. I suspect the logic board thinks that the VGA signal is bad and blanks it at random. When the backlight is on, I can see good VGA image.

I notice that the 5V supply of C739 feeds into U703 (74F14, Schmitt Trigger). My next step is to measure the signal with a scope.

Any hints?
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Old 05-25-2009, 09:30 PM   #14
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Post Re: Has the Dell 1800FP exhibited bad caps?

Quote:
Originally Posted by gyeap
I am rapairing a DELL 1800FP display. The problem is that when VGA signal is connected, the backlight randomly turns on/off about half to several seconds apart.

The logic boad has two caps with high ESR: C739 and C207 as noted by severach. I added parallel capacitors to fix them. However the probelm still persist. C739 measure good 5.0V.

All caps in the power supply board measure good ESR.

The backlight will turn on persistently if the VGA cable is unplugged. This showed that the inverter board is OK. I suspect the logic board thinks that the VGA signal is bad and blanks it at random. When the backlight is on, I can see good VGA image.

I notice that the 5V supply of C739 feeds into U703 (74F14, Schmitt Trigger). My next step is to measure the signal with a scope.

Any hints?
Check the BLON signal to the inverter to see if it varies with the on/off behavior. If it does not, the problem lies on the inverter. If it does, start looking on the signal board.
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Old 05-26-2009, 01:57 AM   #15
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Default Re: Has the Dell 1800FP exhibited bad caps?

eguevarae,

I guess you meant pin 8 of the signal that goes from the logic board to the inverter. The signal will go hi/lo with the backlight on/off. I had figured out that this was the signal that turns on/off the backlight.

When the VGA cable is unconnected, the signal and backlight will stay on. So, the fault should be in the logic board. The pin 8 signal traced to pin 40 of the GENESIS gm5120 chip (pin name GPI0). So, I think the chip is sending the random backlight on/off signal.

I don't have a HDMI signal source to check if this is also affecting the HDMI port. I can't seem to find the schematics of the logic board.
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Old 05-26-2009, 03:44 AM   #16
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Default Re: Has the Dell 1800FP exhibited bad caps?

Quote:
Originally Posted by gyeap
eguevarae,

I guess you meant pin 8 of the signal that goes from the logic board to the inverter. The signal will go hi/lo with the backlight on/off. I had figured out that this was the signal that turns on/off the backlight.

When the VGA cable is unconnected, the signal and backlight will stay on. So, the fault should be in the logic board. The pin 8 signal traced to pin 40 of the GENESIS gm5120 chip (pin name GPI0). So, I think the chip is sending the random backlight on/off signal.

I don't have a HDMI signal source to check if this is also affecting the HDMI port. I can't seem to find the schematics of the logic board.
Hello Gyeap
This link has the same power supply for your monitor but I am unsure about M/Board, you can check it out, it might be yours.
http://www.curto-circuito.com/esquem...B886F_FULL.pdf
bob
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Old 05-26-2009, 09:34 AM   #17
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Default Re: Has the Dell 1800FP exhibited bad caps?

Quote:
Originally Posted by gyeap
eguevarae,
I guess you meant pin 8 of the signal that goes from the logic board to the inverter. The signal will go hi/lo with the backlight on/off. I had figured out that this was the signal that turns on/off the backlight.
Yes. I didn't know which pin, but that's the BLON signal.
Quote:
Originally Posted by gyeap
When the VGA cable is unconnected, the signal and backlight will stay on. So, the fault should be in the logic board. The pin 8 signal traced to pin 40 of the GENESIS gm5120 chip (pin name GPI0). So, I think the chip is sending the random backlight on/off signal.
Agree. I have some monitors with that chip and they make random things.
So what you are telling is that w/o VGA signal, the backlight stays on for the unit to display the "help me! I need signal!" roaming banner? I had a Samsung 17" that did that and it was a small cap on the PSU. Will check my notes and will post back with more info.
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Old 07-21-2009, 11:33 PM   #18
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Default Re: Has the Dell 1800FP exhibited bad caps?

Replace the eeprom ATMEL AT49F001 If you have no video, lamps but no picture or some other weird symptoms it is bad or corrupt. YOu can take it off and read the code and then program into a new one.. Usally we see this bad after the power supply fails and takes out the eeprom prob due to voltage spikes or dirty power. They sell the chip already programmed at www.lcdrepair.us
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Old 07-22-2009, 12:09 AM   #19
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Default Re: Has the Dell 1800FP exhibited bad caps?

Quote:
Originally Posted by LCDrepairllc
Replace the eeprom ATMEL AT49F001 If you have no video, lamps but no picture or some other weird symptoms it is bad or corrupt. YOu can take it off and read the code and then program into a new one.. Usally we see this bad after the power supply fails and takes out the eeprom prob due to voltage spikes or dirty power. They sell the chip already programmed at www.lcdrepair.us
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Old 10-02-2009, 01:31 PM   #20
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Default Re: Has the Dell 1800FP exhibited bad caps?

I have the same problem as gyeap. My backlight works no problem. It is just the the screen turns on and on for a second with VGA and HDMI. My BLON flickers with the LCD. So the logic board is the issue. Was your problem a cap on the power supply or a problem with the logic board?
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